Method of diffusing an impurity into semiconductor wafers

Abstract

A method of diffusing an impurity into semiconductor wafers, wherein the semiconductor wafers and sources of the impurity are arranged in a pressure-reduced vessel or a vacuum vessel with their surfaces opposed, and the vessel is heated to deposit the impurity on the surfaces of the semiconductor wafers and to diffuse the impurity into the wafer surfaces in a separate open vessel, whereby the dispersion or variation of the surface impurity concentrations of the semiconductor wafers is lessened.

What we claim is: 
     
       1. A method of diffusing an impurity into a semiconductor wafer, comprising accommodating a semiconductor wafer and an impurity source in a pressure-reduced vessel such that the wafer and the source are arranged with their surfaces opposed, heating said pressure-reduced vessel so as to deposit the impurity on surface portions of said semiconductor wafer, removing said wafer subjected to the deposition from said vessel, and thereafter heating said wafer so as to diffuse said deposited impurity into said surface portions of said semiconductor wafer. 
     
     
       2. The method of claim 1, wherein said pressure-reduced vessel is hermetically sealed. 
     
     
       3. The method of claim 1, wherein the wafer and the impurity source are planar shaped elements and the opposing surfaces of each element are arranged substantially parallel to each other. 
     
     
       4. The method of claim 1, wherein the impurity source and the semiconductor wafer are arranged closely adjacent to each other. 
     
     
       5. The method of claim 1, wherein the pressure of the vessel is reduced to no more than about 100 Torr., and the pressure-reduced vessel is heated to 850° to 1,150°C for a period of from 10 to 120 minutes. 
     
     
       6. The method of claim 1, wherein the wafer is heated to diffuse said deposited impurity into said surface portions in an open tube. 
     
     
       7. A method of diffusing an impurity into a semiconductor wafer, comprising accommodating a semiconductor wafer and an impurity source in a pressure-reduced vessel, heating said pressure-reduced vessel so as to deposit the impurity on surface portions of said semiconductor wafer, removing said wafer subjected to the deposition from said vessel, and thereafter heating said wafer in an atmosphere containing no impurity. 
     
     
       8. The method of claim 7, wherein said wafer is heated in an atmosphere containing no impurity in an open tube. 
     
     
       9. The method of claim 8, wherein said pressurereduced vessel is hermetically sealed. 
     
     
       10. The method of claim 9, wherein the pressure in said pressure-reduced vessel is no more than about 100 Torr. 
     
     
       11. The method of claim 10, wherein said wafer and said impurity source are planar shaped elements and the opposing surfaces of each element are arranged substantially parallel to each other. 
     
     
       12. The method of claim 11, wherein the impurity source and the semiconductor wafer are arranged closely adjacent to each other. 
     
     
       13. The method of claim 9, wherein said wafer and said impurity source are planar shaped elements and the opposing surfaces of each element are arranged substantially parallel to each other. 
     
     
       14. The method of claim 13, wherein the impurity source and the semiconductor wafer are arranged closely adjacent to each other. 
     
     
       15. The method of claim 7, wherein the impurity is selected from the group consisting of boron, phosphorus and antimony.